1. Field of the Invention
This invention relates to neurotrophic compounds having an affinity for FKBP-type immunophilins, their preparation and use as inhibitors of the enzyme activity associated with immunophilin proteins, and particularly inhibitors of peptidyl-prolyl isomerase or rotamase enzyme activity.
2. Description of the Prior Art
The term immunophilin refers to a number of proteins that serve as receptors for the principal immunosuppressant drugs, cyclosporin A (CsA), FK506, and rapamycin. Known classes of immunophilins are cyclophilins, and FK506 binding proteins, such as FKBP. Cyclosporin A binds to cyclophilin while FK506 and rapamycin bind to FKBP. These immunophilin-drug complexes interface with a variety of intracellular signal transduction systems, especially in the immune system and the nervous system.
Immunophilins are known to have peptidyl-prolyl isomerase (PPIase) or rotamase enzyme activity. It has been determined that rotamase activity has a role in the catalyzation of the interconversion of the cis and trans isomer of immunophilin proteins.
Immunophilins were originally discovered and studied in immune tissue. It was initially postulated by those skilled in the art that inhibition of the immunophilins rotamase activity leads to the inhibition of T-cell proliferation, thereby causing the immunosuppressive action exhibited by immunosuppressive drugs such as cyclosporin A, KF506, and rapamycin. Further study has shown that the inhibition of rotamase activity, in and of itself, is not sufficient for immunosuppressant activity. Schreiber et al., Science, 1990 vol. 250 pp. 556-559. It has been shown that the immunophilin-drug complexes interact with ternary protein targets as their mode of action. Schreiber et al., Cell, 1991, vol. 66, pp. 807-815. In the case of FKBP-FK506 and FKBP-CsA, the drug-immunophilin complexes bind to the enzyme calcineurin, inhibitory T-cell receptor signalling leading to T-cell proliferation. Similarly, the complex of rapamycin and FKBP interacts with the RAFT1/FRAP protein and inhibits signalling from the IL-2 receptor.
Immunophilins have been found to be present at high concentrations in the central nervous system. Immunophilins are enriched 10-50 times more in the central nervous system than in the immune system. Within neural tissues, immunophilins appear to influence neutronal process extension, nitric oxide synthesis, and neurotransmitter release.
It has been found that picomolar concentrations of an immunosuppressant such as KF506 and rapamycin stimulate neurite out growth in PC12 cells and sensory nervous, namely dorsal root ganglion cells (DRGs). Lyons et al., Proc. of Natl. Acad. Sci., 1994 vol. 91, pp. 3191-3195. In whole animal experiments, FK506 has been shown to stimulate nerve regeneration following facial nerve injury and results in functional recovery in animals with sciatic nerve lesions.
Surprisingly, it has been found that drugs with a high affinity for FKBP are potent rotamase inhibitors causing a neurotrophic effect. Lyons et al. These findings suggest the use of immunosuppressants in treating various peripheral neuropathies and enhancing neuronal regrowth in the central nervous system. (CNS). Studies have demonstrated that neurodegenerative disorders such as Alzheimer""s disease, Parkinson""s disease, and amyotrophic lateral sclerosis (ALS) may occur due to the loss, or decreased availability, of a neurotrophic substance specific for a particular population of neurons affected in the disorder.
Several neurotrophic factors effecting specific neuronal populations in the central nervous system have been identified. For example, it has been hypothesized that Alzheimer""s disease results from a decrease or loss of nerve growth factor (NGF). It has thus been proposed to treat Alzheimer""s patients with exogenous nerve growth factor or other neurotrophic proteins such as brain derived nerve factor (BDNF), glial derived nerve factor, ciliary neurotrophic factor, and neurotropin-3 to increase the survival of degenerating neuronal populations.
Clinical application of these proteins in various neurological disease states is hampered by difficulties in the delivery and bioavailability of large proteins to nervous system targets. By contrast, immunosuppressant drugs with neurotrophic activity are relatively small and display excellent bioavailability and specificity. However, when administered chronically, immunosuppressants exhibit a number of potentially serious side effects including nephrotoxicity, such as impairment of glomerular filtration and irreversible interstitial fibrosis (Kopp et al., 1991, J. Am. Soc. Nephrol. 1:162); neurological deficits, such as involuntary tremors, or non-specific cerebral angina such as non-localized headaches (De Groen et al., 1987, N. Engl. J. Med. 317:861); and vascular hypertension with complications resulting therefrom (Kahan et al., 1989 N. Engl. J. Med. 321: 1725).
In order to prevent the side effects associated with use of the immunosuppressant compounds, the present invention provides non-immunosuppressive compounds containing small molecule FKBP rotamase inhibitors for promoting neuronal growth and regeneration in various neuropathological situations where neuronal repair can be facilitated including peripheral nerve damage by physical injury or disease state such as diabetes, physical damage to the central nervous system (spinal cord and brain) brain damage associated with stroke, and for the treatment of neurological disorders relating to neurodegeneration, including Parkinson""s disease, Alzheimer""s disease, and amyotrophic lateral sclerosis.
The present invention relates to a novel class of neurotrophic compounds having an affinity for FKBP-type immunophilins. Once bound to this protein the neurotrophic compounds are potent inhibitors of the enzyme activity associated with immunophilin proteins and particularly rotamase enzyme activity, thereby stimulating neuronal regeneration and outgrowth. A key feature of the compounds of the present invention is that they do not exert any significant immunosuppressive activity in addition to their neurotrophic activity.
A preferred embodiment of this invention is a neurotrophic compound of the formula: 
where
R1 is selected from the group consisting of a C1-C9 straight or branched chain alkyl or alkenyl group optionally substituted with C3-C8 cycloalkyl, C3 or C5 cycloalkyl, C5-C7 cycloalkenyl, Ar1, where said alkyl, alkenyl, cycloalkyl or cycloalkenyl groups may be optionally substituted with C1-C4 alkyl, C1-C4 alkenyl, or hydroxy, where Ar1 is selected from the group consisting of 1-napthyl, 2-napthyl, 2-indolyl, 3-indolyl, 2-furyl, 3-furyl, 2-thiazolyl, 2-thienyl, 3-thienyl, 2-, 3-, 4-pyridyl, and phenyl, having one to three substituents which are independently selected from the group consisting of hydrogen, halo, hydroxyl, nitro, trifuloromethyl, C1-C5 straight or branched alkyl or alkenyl, C1-C4 alkoxy or C1-C4 alkenyloxy, phenoxy, benzyloxy, and amino;
X is selected from the group consisting of oxygen, sulfur, methylene (CH2), or H2;
Y is selected from the group consisting of oxygen or NR2, where R2 is hydrogen or C1-C5 alkyl; and
Z is selected from the group consisting of C2-C5 straight or branched chain alkyl or alkenyl,
wherein the alkyl chain is substituted in one or more positions with Ar1 as defined above, C3-C8 cycloalkyl, cycloalkyl connected by a C1-C5 straight or unbranched alkyl or alkenyl chain, and Ar2 where Ar2 is selected from the group consisting of 2-indolyl, 3-indolyl, 2-furyl, 3-furyl, 2-thiazolyl, 2-thienyl, 3-thienyl, 2-, 3-, or 4-pyridyl, and phenyl, having one to three substituents which are independently selected from the group consisting of hydrogen, halo, hydroxyl, nitro, trifuloromethyl, C1-C6 straight or branched alkyl or alkenyl, C1-C4 alkoxy or C1-C4 alkenyloxy, phenoxy, benzyloxy, and amino; Z may also be the fragment: 
where
R3 is selected from the group consisting of straight or branched alkyl C1-C3 optionally substituted with C3-C5 cycloalkyl, or Ar1 as defined above, and unsubstituted Ar1;
X2 is O or NR5, where R5 is selected from the group consisting of hydrogen, C1-C5 straight or branched alkyl and alkenyl;
R4 is selected from the group consisting of phenyl, benzyl, C1-C5 straight or branched alkyl or alkenyl, and C1-C5 straight or branched alkyl or alkenyl substituted with phenyl; or pharmaceutically acceptable salts or hydrates thereof.
Another preferred embodiment of this invention is a neurotrophic compound of the formula: 
where
R1 is a C1-C9 straight or branched chain alkyl or alkenyl group optionally substituted with C3-C5 cycloalkyl, C3 or C5 cycloalkyl, C5-C7 cycloalkenyl, or Ar1, where said alkyl, alkenyl, cycloalkyl or cycloalkenyl groups may be optionally substituted with C1-C4 alkyl, C1-C4 alkenyl, or hydroxy, and where Ar1 is selected from the group consisting of 1-napthyl, 2-napthyl, 2-indolyl, 3-indolyl, 2-furyl, 3-furyl, 2-thiazolyl, 2-thienyl, 3-thienyl, 2-, 3-, or 4-pyridyl, or phenyl, having one to three substituents which are independently selected from the group consisting of hydrogen, halo, hydroxyl, nitro, trifuloromethyl, C1-C5 straight or branched alkyl or alkenyl, C1-C4 alkoxy or C1-C4 alkenyloxy, phenoxy, benzyloxy, and amino;
Z is a C2-C5 straight or branched chain alkyl or alkenyl, wherein the alkyl chain is substituted in one or more positions with Ar1 as defined above, C3-C5 cycloalkyl, cycloalkyl connected by a C1-C5 straight or unbranched alkyl or alkenyl chain, or Ar2 where Ar2 is selected from the group consisting of 2-indolyl, 3-indolyl, 2-furyl, 3-furyl, 2-thiazolyl, 2-thienyl, 3-thienyl, 2-, 3-, or 4-pyridyl, or phenyl, having one to three substituents which are independently selected from the group consisting of hydrogen, halo, hydroxyl, nitro, trifuloromethyl, C1-C5 straight or branched alkyl or alkenyl, C1-C4 alkoxy or C1-C4 alkenyloxy, phenoxy, benzyloxy, and amino; or pharmaceutically acceptable salts or hydrates thereof.
Another preferred embodiment of the invention is a neurotrophic compound having an affinity for FKBP-type immunophilins which inhibit the rotamase activity of the immunophilin.
Another preferred embodiment of the present invention is a method for treating a neurological disorder in an animal comprising administering a therapeutically effective amount of a compound having an affinity for FKBP-type immunophilins which inhibits the rotamase activity of the immunophilin.
Another preferred embodiment of the invention is a method of promoting neuronal regeneration and growth in mammals, comprising administering to a mammal an effective amount of a neurotrophic compound having an affinity for FKBP-type immunophilins which inhibits the rotamase activity of the immunophilin.
Yet another preferred embodiment of the invention is a method of preventing neurodegeneration in an animal comprising administering to an animal an effective amount of a neurotrophic compound having an affinity for FKBP-type immunophilins which inhibits rotamase activity of the immunophilin.
Another preferred embodiment is a neurotrophic N-glyoxyl prolyl ester compound of the formula: 
where
R1 is a C1-C5 straight or branched chain alkyl or alkenyl group optionally substituted with C3 to C6 cycloalkyl, or Ar1, where Ar1 is selected from the group consisting of 2-furyl, 2-thienyl, or phenyl;
X is selected from the group consisting of oxygen and sulfur;
Y is oxygen; and
Z is a straight or branched chain alkyl or alkenyl, wherein the alkyl chain is substituted in one or more positions with Ar1 as defined above, C3-C6 cycloalkyl, Ar2 where Ar2 is selected from the group consisting of 2-, 3-, or 4-pyridyl, or phenyl, having one to three substituents which are independently selected from the group consisting of hydrogen and C1-C4 alkoxy.
Particularly preferred neurotrophic N-glyoxyl prolyl ester compounds according to the above formula are selected from the group consisting of:
3-(2,5-dimethoxyphenyl)-1-propyl (2S)-1-(3,3-dimethyl-1, 2-dioxopentyl)-2-pyrrolidinecarboxylate,
3-(2,5-dimethoxyphenyl)-1-prop-2-(E)-enyl (2S)1-(3,3-dimethyl-1,2-dioxopentyl)-2-pyrrolidine-carboxylate.
2-(3,4,5-trimethoxyphenyl)-1-ethyl (2S)-1-(3,3-dimethyl-1,2-dioxopentyl)-2-pyrrolidinecarboxylate,
3-(3-Pyridyl)-1-propyl (2S)-1-(3,3-dimethyl-1,2-dioxopentyl)-2-pyrrolidinecarboxylate,
3-(2-Pyridyl)-1-propyl (2S)-1-(3,3-dimethyl-1,2-dioxopentyl)-2-pyrrolidinecarobxylate,
3-(4-Pyridyl)-1-propyl (2S)-1-(3,3-dimethyl-1,2-dioxopentyl)-2-pyrrolidinecarboxylate,
3-phenyl-1-propyl (2S)-1-(2-tert-butyl-1,2-dioxoethyl)-2-pyrrolidinecarboxylate,
3-phenyl-1-propyl (2S)-1-(2-cyclohexylethyl-1,2-dioxoethyl)-2-pyrrolidinecarobxylate,
3-(3-pyridyl)-1-propyl (2S)-1-(2-cyclohexylethyl-1,2-dioxoethyl)-2-pyrrolidinecarboxylate,
3-(3-pyridyl)-1-propyl (2S)-1-(2-tert-butyl-1,2-dioxoethyl)-2-pyrrolidinecarboxylate,
3,3-diphenyl-1-propyl (2S)-1-(3,3-dimethyl-1,2-dioxopentyl)-2-pyrrolidinecarobxylate,
3-(3-pyridyl)-1-propyl (2S)-1-(2-cyclohexyl-1,2-dioxcethyl)-2-pyrrolidinecarboxylate,
3-(3-Pyridyl)-1-propyl (2S)-N-([2-thienyl] glyoxyl)pyrrolidinecarboxylate,
3,3-Diphenyl-1-propyl (2S)-1-(3,3-dimethyl-1,2-dioxobutyl)-2-pyrrolidinecarboxylate,
3,3-Diphenyl-1-propyl (2S)-1-cyclohexylglyoxyl-2-pyrrolidinecarboxylate, and
3,3-Diphenyl-1-propyl (2S)-1-(2-thienyl)glyoxyl-2-pyrrolidinecarboxylate.